Northern Ireland Chalk nomenclature (Ulster Cretaceous Province) - Hibernian Greensands Group: Island Magee Siltstones Formation

Name

The Island Magee Siltstones Member was first used in Griffith and Wilson (1982). The term is upgraded to formation status herein.

Type section

Collin Glen [J 269 702] (Belfast area), Cloghfin [J 483 938] (Carrickfergus area), Magheramorne area [J 430 980] (Larne area).

Primary Reference Section

Kilcoan Old Quarry [J 4610 9850] and numerous localities on the Larne, Antrim, Carrickfergus and Belfast sheet areas (see Griffith and Wilson (1982), Page 48, Figure 16A).

Formal subdivisions

None

Definition of upper boundary

Disconformable with the Collinwell Sands Formation and unconformable with the Kilcoan Sands Formation beneath the so-called Turonian non-sequence of the Hibernian Greensands Group.

Definition of lower boundary

Conformable with Belfast Marls Formation with the boundary arbitrarily taken at the base of the first upwardly occurring hard calcareous siltstone above the transitional top of the preceding formation.

Lithology

Hard and soft grey siltstones and marls (calcareous siltstones) that weather to a pale yellow colour.

Distribution

East Antrim Basin and the Southern Uplands area of Northern Ireland.

Thickness

A maximum of 8.0m in the Magheramorne area and a minimum of 0.67m over the Knockagh Axis north of Belfast.

Previous names

The Grey Marls and Yellow Sandstones with Chert of Tate (1865) and Reid (1971); Yellow Sandstones of Hume (1897) and Hancock (1961); Yellow Sandstones and Grey Marls of Manning, Robbie and Wilson (1970).

Island Magee Siltstones Member.

Parent

Hibernian Greensands Group.

Age and biostratigraphy

Upper Cretaceous, Cenomanian. Acanthoceras rhotomagense Zone.

References

Griffith and Wilson (1982).